I'm really paranoid, because I had my wallet stolen once and my whole purse stolen once while I was living in Chicago (not on a plane) and the effort it took to fix the damage the thief did with my credit cards and checkbook took months to straighten out. It was an unbelievable hassle. I now always take my purse to the lav with me in airplanes, and I never, ever put my laptop in an overhead bin but always under the seat in front of me.

I read a story once about a guy who put his laptop in an overhead bin several rows ahead of his seat, and when he went to retrieve it, it was gone. He did run down the airport corridor after deplaning and spotted a woman with his laptop bag. She gave it back to him and kept walking--she made it obvious that she just didn't mistake his bag for hers, as she didn't head back toward the plane.